The present invention relates generally to the field of avionics for collision avoidance systems (CAS). More specifically, the present invention relates generally to airborne traffic alert and collision avoidance systems and transponders. The collision avoidance system described herein has the capability to position and separate aircraft in a large flight formation in, for example, night/instrument meteorological conditions.
Spurred by the collision of two airliners over the Grand Canyon in 1956, the airlines initiated a study of collision avoidance concepts. By the late 1980""s, a system for airborne collision avoidance was developed with the cooperation of the airlines, the aviation industry, and the Federal Aviation Administration (FAA). The system, referred to as Traffic Alert and Collision Avoidance System II (TCAS II) was mandated by Congress to be installed on most commercial aircraft by the early 1990""s. A chronology of the development of airborne collision avoidance systems can be found in xe2x80x9cIntroduction to TCAS II,xe2x80x9d printed by the Federal Aviation Administration of the U.S. Department of Transportation, March 1990.
The development of an effective airborne CAS has been the goal of the aviation community for many years. Airborne collision avoidance systems provide protection from collisions with other aircraft and are independent of ground based air traffic control. As is well appreciated in the aviation industry, avoiding such collisions with other aircraft is a very important endeavor. Furthermore, collision avoidance is a problem for both military and commercial aircraft alike. In addition, a large, simultaneous number of TCAS interrogations from close-in formation aircraft members generate significant radio frequency (RF) interference and could potentially degrade the effectiveness of maintaining precise position/separation criteria with respect to other aircraft and obstacles. Therefore, to promote the safety of air travel, systems that avoid collision with other aircraft are highly desirable.
In addition the problems described above, it is desirable that aircraft, specifically military aircraft, perform precision airdrops, rendezvous, air refueling, and air-land missions at night and in all weather conditions, including Instrument Meteorological Conditions (IMC) with a low probability of detection. Also, it is desirable that these aircraft be allowed as few as 2 through as many as 250 aircraft to maintain formation position and separation at selectable ranges from 500-ft to 100-nm at all Instrument Flight Rules (IFR) altitudes as described in the Defense Planning Guidelines. Also, the system is to be compatible (primarily because of cost issues) with current station keeping equipment (SKE) systems or they will not be able to fly IMC formation with SKE-equipped aircraft.
Referring to FIG. 1, there is shown a block diagram of a conventional TCAS system. Shown in FIG. 1 are TCAS directional antenna 10, TCAS omni-directional antenna 11, and TCAS computer unit 12, which includes receiver 12A, transmitter 12B, and processor 12C. Also shown are aural annunciator 13, traffic advisory (TA) display 14, and resolution advisory displays 15. Alternatively, the TA and RA displays are combined into one display (not shown). The transponder is comprised of transponder unit 16A, control panel 16B, and transponder antennas 16C and 16D. The TCAS and transponder operate together to function as a collision avoidance system. Those skilled in the art understand that this is merely illustrative of a conventional TCAS. For example, many other configurations are possible such as replacing omni-directional antenna 11 with a directional antenna as is known to those skilled in the art. The operation of TCAS and its various components are well known to those skilled in the art and are not necessary for understanding the present invention.
In a TCAS system, both the interrogator and transponder are airborne and provide a means for communication between aircraft. The transponder responds to the query by transmitting a reply that is received and processed by the interrogator. Generally, the interrogator includes a receiver, an analog to digital converter (A/D), a video quantizer, a leading edge detector, and a decoder. The reply received by the interrogator consists of a series of information pulses which may identify the aircraft, or contain altitude or other information. The reply is a pulse position modulated (PPM) signal that is transmitted in either an Air Traffic Control Radar Beacon System (ATCRBS) format or in a Mode-Select (Mode-S) format.
A TCAS II equipped aircraft can monitor other aircraft within approximately a 20 mile radius of the TCAS II equipped aircraft. (U.S. Pat. No. 5,805,111, Method and Apparatus for Accomplishing Extended Range TCAS, describes an extended range TCAS.) When an intruding aircraft is determined to be a threat, the TCAS II system alerts the pilot to the danger and gives the pilot bearing and distance to the intruding aircraft. If the threat is not resolved and a collision or near miss is probable, then the TCAS II system advises the pilot to take evasive action by, for example, climbing or descending to avoid a collision.
In the past, systems in addition to those described above have been developed to provide collision avoidance for aircraft flying in formation. One type of system is provided by AlliedSignal Aerospace and is known as Enhanced Traffic Alert Collision Avoidance System (ETCAS). The ETCAS provides a normal collision avoidance and surveillance, and a formation/search mode for military specific missions.
The AlliedSignal ETCAS falls short in several ways. First, once an aircraft joins the formation, the ETCAS does not itself or in conjunction with any other on-board system maintain aircraft position and separation within the formation. The ETCAS is simply a situational awareness tool that designates formation members by receiving the Mode 3/A code transmitted from the plane""s transponder; the ETCAS does not interface with other aircraft systems to compensate for formation position errors. The ETCAS is actually an aircraft formation member identification and rendezvous system that falls short as a true intra-formation positioning collision avoidance system. Second, the ETCAS Vertical Speed Indicator/Traffic Resolution Alert (VSI/TRA) display does not annunciate relative velocity (range-rate) of the lead formation and member aircraft. The ETCAS is only marginally effective without relative velocity of formation aircraft annunciated on the VSI/TRA display. Hence, the pilot has no relative velocity reference to maintain formation position with the lead aircraft, especially during critical turning maneuvers. Third, the ETCAS formation/search mode technique is wholly based upon active TCAS interrogations. Transponder interrogations and the resulting Mode-S transponder replies significantly increase RF reception interference with a large formation of aircraft and could degrade the effectiveness of maintaining precise position/separation criteria. In addition, the increased composite level of RF severely inhibits a large formation from covertly traversing airspace undetected.
Another problem is presented in previous systems wherein station keeping equipment (SKE) on existing military aircraft can support a formation of only 16 aircraft.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention, and is not intended to be a full description. A full appreciation of the various aspects of the invention can only be gained by taking the entire specification, claims, drawings, and abstract as a whole.
The present invention describes a system and method of maintaining aircraft position and safe separation of a large aircraft flying formation, such as those types of military formations to perform a strategic brigade airdrop, although it can be used for any aeronautical service involving the application of aircraft formation flying units. The present invention involves the use of a passive Traffic Alert and Collision Avoidance System (TCAS) and Mode-S data link transponder to provide distributed intra-formation control among multiple cells of formation aircraft.
In one embodiment, the present invention comprises a data link Mode-S transponder, which generates and transmits ADS-B broadcast data. Such ADS-B broadcast data contains aircraft position information of the host aircraft. The present invention also includes a passive traffic alert and collision avoidance system (TCAS) computer in communication with the Mode-S transponder. The TCAS receives and processes broadcast data from another data link transponder that is located onboard another aircraft (e.g., a follower aircraft within a cell) to determine relative aircraft position of the host aircraft with respect to the other aircraft.
In a further embodiment of the present invention, a data link Mode-S transponder is in communication with a TCAS computer. The TCAS computer receives and processes the broadcast data from the transponder. The TCAS computer is also in communication with a flight mission computer, which receives the broadcast data from the TCAS computer and generates steering commands based on the broadcast data. The present invention includes a high-speed digital communication link that is operatively connected to the mission computer, which is used to transmit the steering commands to one other transponder-equipped aircraft where the steering commands are processed by the other aircraft. The other aircraft uses the steering commands to position itself with respect to the host aircraft. This can be accomplished either with station keeping equipment or automatic flight controllers.
The method of the present invention includes the steps of providing a transponder (on one or more aircraft), which generates and transmits ADS-B broadcast data to determine relative aircraft position, and providing a TCAS computer onboard a host aircraft. The TCAS is in communication with the transponder and receives and processes ADS-B broadcast data from the transponder. The method includes the step of (automatically) positioning and separating the aircraft with respect to one another while flying in formation based on the broadcast data using, for example, automatic flight or station keeping means. The method further includes the steps of providing a mission computer in communication with the TCAS computer; transmitting the broadcast data from the TCAS computer to the mission computer; processing the broadcast data; and selectively transmitting the processed broadcast data between the aircraft via a high speed data link. The step of processing further includes the step of calculating the target aircraft range, range rate, relative altitude, altitude rate, and bearing from the broadcast (ADS-B) data received from the Mode-S transponder to determine whether an aircraft is intruding upon the air space of the TCAS-equipped aircraft. The step of selectively transmitting is conducted, for example, using a unique flight identifier of the particular aircraft. The method also includes the steps of alerting the pilot of the aircraft when an intruder penetrates a predefined perimeter of aircraft flying in formation and displaying the range rate or relative velocity of the aircraft within a predefined cell or airspace. The method further includes the step of inhibiting air traffic control radar beacon systems (ATCRBS) messages from being sent by the Mode-S transponder.
The present invention is capable of supporting a flight formation of 250 aircraft through distributed control of multiple aircraft formation cell units. It uses a passive surveillance technique for maintaining formation aircraft position within 500-ft to 100-nm of one another at all Instrument Flight Rules (IFR) altitudes. Updated aircraft position information is broadcast periodically (e.g., 2 times per second). These periodic Mode-S transponder transmissions of Automatic Dependent Surveillance Broadcast (ADS-B) information are sent to and received by the TCAS of other TCAS-equipped aircraft. This extended ADS-B data transmission is also referred to herein as Global Positioning System (GPS) or Mode-S squitter. Aircraft positions, relative altitude and velocity are presented on the Vertical Speed Indicator/Traffic Resolution Advisory (VSI/TRA) display (e.g., cathode ray tube or flat panel display) and processed in the aircraft mission computer""s intra-formation positioning collision avoidance system (IFPCAS) data fusion center. The mission computer receives data from the TCAS computer, processes the data to obtain, for example, range and range rate, and then the mission computer places the data in a format usable by external equipment such as the station keeping equipment. Steering commands are generated and disseminated to the various or individual formation aircraft. The steering commands are executed using on-board station keeping equipment (which can also be used to maintain helicopter positioning) or autopilot means. The passive surveillance technique of the present invention significantly reduces the range upon which a large aircraft formation can be detected and the resulting lower RF interference maintains uninterrupted position and separation correction updates.
The present invention overcomes several problems, including, but not limited to: providing a means to position and separate aircraft in an extremely large flight formation (e.g., 100 aircraft) in night/instrument meteorological conditions utilizing ADS-B information and high frequency data links (and accompanying antennas) for disseminating intra-formation steering commands; utilizing the aircraft mission computer as a data fusion center for generating steering commands based upon assimilated ADS-B information received from the TCAS; and reducing the amount of RF interference resulting from multiple simultaneous TCAS interrogations and Mode-S transponder replies. The present invention maintains safe separation between 2 to 100 aircraft, and up to 250 aircraft, in night and Instrument Meteorological Conditions (IMC). The present invention enables aircraft position/separation at selectable ranges from 500-ft to 100-nmi at all Instrument Flight Rules (IFR) altitudes. The present invention is an integrated aircraft positioning/separation control solution.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the following detailed description of the invention or can be learned by practice of the present invention. It should be understood, however, that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only because various changes and modifications within the spirit and scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.
The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.
FIG. 1 (prior art) is a block diagram of a conventional TCAS system.
FIG. 2 is a diagram of the components of an exemplary aircraft formation.
FIG. 3 is a block diagram of an embodiment of the collision avoidance system for close formation flights in accordance with the present invention.
FIG. 4 is a block diagram of an alternate embodiment of the collision avoidance system for intra-formation positioning flights in accordance with the present invention.
FIG. 5 is a more detailed block diagram of the embodiment of FIG. 4 (the intra-formation collision avoidance system architecture) in accordance with the present invention.
FIG. 6 is an elevation of a TCAS VSI/TRA display with the relative velocity (range rate) of formation aircraft displayed in accordance with the present invention.
FIG. 7 is a flowchart of the methodology used to display information to the viewer in accordance with the present invention.
FIG. 8 is a flowchart of the methodology used to display information to the viewer in accordance with the present invention.
FIG. 9 is a flowchart of the methodology used to display information the to viewer in accordance with the present invention.
FIG. 10 is a flowchart of the methodology used to display information to the viewer in accordance with the present invention.